1. Field of the Invention
The present invention generally relates to ultrasound imaging devices in medicine, and particularly relates to an ultrasound imaging device in medicine displaying a freeze-frame of an ultrasound image.
2. Description of the Prior Art
FIG. 1 shows a block diagram of an ultrasound imaging device in medicine of the prior art. In FIG. 1, the ultrasound imaging device comprises an ultrasound scanning unit 100, a video signal node 10, an image switch circuit 11, a display device 12, a recording and reproducing device 14, an image store circuit 15, a control circuit 16, and a keyboard 17.
A video signal of images for diagnostic purposes which is provided by the ultrasound scanning unit 100 is applied to the node 10, and, thence, provided for the image switch circuit 11. From a plurality of video signal inputs, an image switch circuit 11 selects one video signal for its output, which is supplied to the display device 12 for displaying image data for diagnosis. At the same time, the same video signal output from the image switch circuit 11 is provided for the recording and reproducing device 14 for recording the collected images.
In a reproducing mode of the device, the recording and reproducing device 14 reproduces a video signal of diagnosis images, which signal is then supplied to the image switch circuit 11 and to the image store circuit 15. The image store circuit 15 digitizes a received video signal, and stores the digitized data into a frame memory thereof. Also, the image store circuit 15 in a reproducing mode sequentially reads out image data from the frame memory, and transforms it into an analog signal to provide for the image switch circuit 11.
The control circuit 16 controls the switching of the image switch circuit 11 according to instructions given through operations on the keyboard 17. Controlled by the control circuit 16, the image switch circuit 11 selects a video signal output from the plurality of video signal inputs provided from the node 10, the recording and reproducing device 14, and the image store circuit 15. Also, the control circuit 16 controls the operation of the recording and reproducing device 14 and the write operation of the image store circuit 15. The image store circuit 15 carries out a write operation and a read operation on the frame memory.
When an instruction to display a freeze-frame is given by the keyboard 17, the control circuit 16 orders the image store circuit 15 to stop writing data into the frame memory. The image store circuit 15 stops writing as instructed, but continues to read out image data form the frame memory. Since this image data stays the same without being rewritten, the image store circuit 15 outputs a video signal of the same image, i.e., a freeze-frame. In this situation, the display device 12 shows a freeze-frame.
FIG. 2 is an illustrative drawing showing the operation of the ultrasound imaging device operating in the B-mode to provide cross-section images. When a time length required for the scanning of one image, i.e., an ultrasound scan frame period, is odd number times (at least three times) as long as the field period of a video signal, frames of ultrasound scanning images as shown at the bottom of FIG. 2 are displayed on the display device 12. In FIG. 2, E denotes an even number field, and 0 an odd number field.
When an instruction to freeze the display image is given at a time t1 while ultrasound images shown in FIG. 2 are being reproduced from the recording and reproducing device 14, a freeze-frame without flickering is displayed because an odd number field and an even number field of the same image are repeatedly displayed one after another. Those two fields are of the same image corresponding to a frame N+1 because the instruction is given at an instance when the frame memory contains the two fields of the frame N+1 as the last two stored fields.
However, when an instruction to freeze the display image is given at a time to, a freeze-frame with flickering will be displayed because an odd number field and an even number field of different images are repeatedly displayed one after another. Those two fields are from different images because the instruction is given at an instance when the frame memory contains an odd number field of a frame N-1 and an even number field of the frame N as the last two stored fields.
Accordingly, there is a need in the field of ultrasound imaging devices in medicine for an ultrasound imaging device which can prevent a displayed freeze-frame from flickering.